Golf ball core compositions

ABSTRACT

The present invention is directed to improved polybutadiene compositions suitable for use in molded golf ball core construction. The improved polybutadiene compositions are composed of polypropylene powder resins which have the effect of increasing the hardness of the resulting molded cores without increasing the weight upon curing, thereby allowing for a reduction in the amount of crosslinking agents utilized and increasing the amount of fillers incorporated therein. The addition of the polypropylene powder resins to the core compositions lowers the cost of the molded core, while maintaining the proper weight and compression. The present invention is also directed to golf balls produced utilizing the improved core compositions.  
     Furthermore, the invention is directed to a method for reducing the amount of crosslinking agents utilized to formulate a core composition through the incorporation of polypropylene powder resins. In addition, a method for decreasing the amount of crosslinking agents and increasing the amount of mineral fillers included in a core composition through the incorporation of polypropylene powder resins is also disclosed.

[0001] This is a continuation-in-part of U.S. application Ser. No.07/874,066, filed on Apr. 24, 1992.

BACKGROUND OF THE INVENTION

[0002] The present invention is directed to improved polybutadienecompositions for use in molded golf ball core construction. The improvedpolybutadiene compositions contain polypropylene powder resins, whichhave the effect of increasing the hardness of the resulting molded coreswithout increasing the weight and/or substantially reducing theresiliency of the ball. The present invention is also directed to golfballs produced utilizing the improved core compositions.

[0003] Moreover, it has been found that the addition of the particulatepolypropylene allows for a reduction in the amount of crosslinkingagents utilized in the core compositions and/or an increase in theamount of higher specific gravity fillers, thereby dramaticallydecreasing the cost of the golf ball cores. A method for producing suchan effect is also disclosed.

[0004] Two of the principal properties involved in the performance ofgolf balls are resilience and hardness. Resilience is determined by thecoefficient of restitution (C.O.R.), the constant “e”, which is theratio of the relative velocity of two elastic spheres after directimpact to that before impact, or more generally, the ratio of theoutgoing velocity to incoming velocity of a rebounding ball. As aresult, the coefficient of restitution (i.e. “e”) can vary from zero toone, with one being equivalent to an elastic collision and zero beingequivalent to an inelastic collision. Hardness is determined as thedeformation (i.e. compression) of the ball under various load conditionsapplied across the ball's diameter (i.e. the lower the compressionvalue, the harder the material).

[0005] Resilience (C.O.R.), along with additional factors such asclubhead speed, angle of trajectory, and ball configuration (i.e. dimplepattern), generally determines the distance a ball will travel when hit.Since clubhead speed and the angle of trajectory are not factors easilycontrollable, particularly by golf ball manufacturers, the factors ofconcern among manufacturers are the coefficient of restitution (C.O.R.)and the surface configuration of the ball.

[0006] In this regard, the coefficient of restitution of a golf ball isgenerally measured by propelling a ball at a given speed against a hardsurface and measuring the ball's incoming and outgoing velocityelectronically. The coefficient of restitution must be carefullycontrolled in all commercial golf balls in order for the ball to bewithin the specifications regulated by the United States GolfersAssociation (U.S.G.A.). Along this line, the U.S.G.A. standards indicatethat a “regulation” ball cannot have an initial velocity (i.e. the speedoff the club) exceeding 255 feet per second (250 feet per second with a2% tolerance). Since the coefficient of restitution of a ball is relatedto the ball's initial velocity (i.e. as the C.O.R. of a ball isincreased, the ball's initial velocity will also increase), it is highlydesirable to produce a ball having a sufficiently high coefficient ofrestitution to closely approach the U.S.G.A. limit on initial velocity,while having an ample degree of hardness (i.e. impact resistance) toproduce enhanced durability.

[0007] The coefficient of restitution (C.O.R.) in solid core balls is afunction of the composition of the molded core and of the cover. Inballs containing a wound core (i.e. balls comprising a liquid or solidcenter, elastic windings, and a cover), the coefficient of restitutionis a function of not only the composition of the center and cover, butalso the composition and tension of the elastomeric windings.

[0008] The present invention relates to the addition of a polypropylenepowder resin to polybutadiene core compositions, such as those disclosedin U.S. Pat. Nos. 4,726,590; 4,838,556; 4,844,471; and 4,852,884 inorder to produce solid golf ball cores and/or centers exhibitingenhanced hardness without an increase in weight and a substantialreduction in C.O.R. It has been found that the addition of apolypropylene powder resin results in a core which is too hard (i.e.exhibits low compression) and thus allows for a reduction in the amountof crosslinking agent utilized to soften the core to a normalcompression.

[0009] Furthermore, because polypropylene powder resin can be added tocore composition without an increase in weight of the molded core uponcuring, the addition of the polypropylene powder allows for the additionof large amounts of higher specific gravity fillers, such as mineralfillers. Since the crosslinking agents utilized in the polybutadienecore compositions are expensive and/or the higher specific gravityfillers are relatively inexpensive, the addition of the polypropylenepowder resin substantially lowers the cost of the golf ball cores whilemaintain proper weight and compression.

[0010] Along these lines, although other particulate thermoplasticmaterials have been evaluated, including relatively low specific gravitythermoplastic powders (i.e. polystyrene, polyethylene, polymethylmethacrylate, etc.), it has been found that these powdered resins do notincrease the hardness of the cores to the degree desired, thus stillrequiring use of larger amounts of the expensive crosslinking agentssuch as zinc diacrylate, and/or they reduce the C.O.R. values toundesirable ranges. Furthermore, the alternative thermoplastic powderresins produce, when compounded, heavier cores than the presentinvention. Consequently, the addition of the inexpensive mineral fillersis substantially limited in the powdered plastics in comparison to thepresent invention.

[0011] Accordingly, it is an object of the present invention to provideimproved polybutadiene core compositions which, when utilized toformulate golf balls, produce golf balls exhibiting enhanced hardness ata lower weight due to the composition of the core. An additional objectof the invention is to provide cores or centers for the construction ofsolid or wound golf balls which dramatically lower the cost of the golfball while maintaining proper weight and compression. Furthermore, sincea golf ball produced in accordance with the present invention exhibitsan enhanced hardness at a lower weight, it is possible to increase thedurability of the ball by adding additional durability enhancers withoutgreatly sacrificing the ball's overall weight and/or composition. Astill further object of the invention is to produce golf ball cores orcenters which maintain their roundness and shape upon continued impactby a golf club.

[0012] These and other objects and features of the invention will beapparent from the following summary and description of the invention andfrom the claims.

SUMMARY OF THE INVENTION

[0013] In one aspect, the present invention is directed to an improvedcomposition for golf ball core production comprising a base elastomerselected from polybutadiene and mixtures of polybutadiene with otherelastomers, at least one metallic salt of an unsaturated carboxylic acid(a co-crosslinking agent), a free radical initiator (a co-crosslinkingagent) and a polypropylene powder resin. In addition, suitable andcompatible modifying ingredients including, but not limited to, metaloxide activators, fatty acids, fillers and other additives may beincluded.

[0014] In an additional aspect, the present invention relates to a golfball comprising a solid core and a cover therefor, the solid coreconsisting of a base elastomer selected from polybutadiene and mixturesof polybutadiene with other elastomers, at least one metallic salt of anunsaturated carboxylic acid, a free radical initiator and a particulatepolypropylene powder, and the cover comprising one or more layers ofionomer resin-based compositions.

[0015] In a further aspect, the present invention is directed to amethod for reducing the amount of crosslinking agent utilized toformulate a core composition through the incorporation of apolypropylene powder resin. In a still further aspect, a method fordecreasing the amount of a crosslinking agent and increasing the amountof mineral fillers in a core composition through the incorporation of apolypropylene powder resin is also disclosed.

[0016] Further scope of the applicability of the invention will becomeapparent from the detailed description provided below.

DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention is directed to improved core compositionswhich, when utilized for golf ball core construction, produce coresexhibiting enhanced hardness without an increase in weight and/or adecrease in resilience. In this regard, it has been found that theaddition of a polypropylene powder resin to polybutadiene corecompositions has the effect of increasing the hardness of the resultantcores.

[0018] In addition, the present invention is directed to the discoverythat the particulate polypropylene powder can be added to variouspolybutadiene core compositions as a cost effective means of loweringcompression (i.e. hardness) of the molded cores. Since the addition ofthe polypropylene powder produces cores that are too hard, a substantialreduction in the use of expensive crosslinking agents, such as zincdiacrylate, can be achieved in order to soften the center to a normalcompression.

[0019] Furthermore, because the specific gravity of polypropylene isvery low (0.90 g/cm³) and the polypropylene powders produce a lighterweight molded core upon curing, large amounts of higher specificgravity, less expensive, mineral fillers such as calcium carbonate canbe utilized. As a result, the addition of the particulate polypropylenepowder dramatically lowers the cost of the core composition whilemaintaining the weight and compression desired.

[0020] The polypropylene (C₃H₅) powder suitable for use in the presentinvention has a specific gravity of about 0.90 g/cm³, a melt flow rateof about 4 to about 12 and a particle size distribution of greater than99% through a 20 mesh screen. Examples of such polypropylene powderresins include those sold by the Amoco Chemical Co., Chicago, Ill.,under the designations “6400 P”, “7000 P” and “7200 P”. The typicalproperties of these resins are listed below: Properties of Resin 6400 P7000 P 7200 P Melt flow rate, ASTM D1238, 2.16 kg at 4 10 12 230° C.Density, ASTM D792 at 23° C. g/cm³ 0.90 0.90 0.90 Particle sizedistribution, ASTM D1921 0 0 0 12 screen mesh, % retained >99 >99 >99smaller than 140 screen mesh, % <1 <1 <1

[0021] In general, polypropylene (unfilled) possess the followingproperties: ASTM test Polypropylene Properties method Unfilled  1.Melting temperature, ° C. 160-175 T_(m), (crystalline)  2. Processingtemperature range, ° F. I: 400-550 (C = compression; T = transfer; E:400-500 I = Injection; E = extrusion)  3. Molding pressure range, 10³p.s.i. 10-20  4. Compression ratio 2.0-2.4  5. Hold (linear) shrinkage,in./in. D955 0.010-0.025  6. Tensile strength at break, p.s.i. D6384500-6000  7. Elongation at break, % D638 100-600  8. Tensile yieldstrength, p.s.i. D638 4500-5400  9. Compressive strength (rupture oryield), p.s.i. D695 5500-8000 10. Flexural strength (rupture or yield),p.s.i. D790 6000-8000 11. Tensile modulus, 10³ p.s.i. D638 165-225 12.Compressive modulus, 10³ p.s.i. D695 150-300 13. Flexural modulus, 10³p.s.i 73° F. D790 170-250 200° F. D790 50 250° F. D790 35 300° F. D79014. Izod Impact, ft.-lb./in. of notch D2S6A 0.4-1.2 (1/4-in, thickspecimen) 15. Hardness Rockwell D785 R80-102 Shore/Barcol D2240/2583316. Coef. of linear thermal expansion, D696  81-100 10⁻⁶ in./in. ° C.17. Deflection temperature 264 p.s.i. D648 120-140 under flexural load,° F. 66 p.s.i. D648 225-250 18. Thermal conductivity, 10⁻⁴ cal.-cm./C177 2.8 sec..cm.²° C. 19. Specific gravity D792 0.900-0.910 20. Waterabsorption (1/8-in. 24 hr. D570 0.01-0.03 thick specimen), % SaturationD570 21. Dielectric strength (1/8-in. D149 600 thick specimen), shorttime, v./mil

[0022] It has been found that the addition of polypropylene inparticulate form, such as polypropylene powder resins, substantiallyenhances the desired properties of the core compositions over known golfball core additives including other known thermoplastic polymers inpowdered form.

[0023] The core compositions and resulting molded golf balls of thepresent invention containing the particulate polypropylene resins aremanufactured using conventional ingredients and techniques. In thisregard, the core compositions of the invention may be based onpolybutadiene, and mixtures of polybutadiene with other elastomers. Itis preferred that the base elastomer have a relatively high molecularweight. The broad range for the molecular weight of suitable baseelastomers is from about 50,000 to about 500,000. A more preferred rangefor the molecular weight of the base elastomer is from about 100,000 toabout 500,000. As a base elastomer for the core composition,cis-polybutadiene is preferably employed, or a blend ofcis-polybutadiene with other elastomers may also be utilized. Mostpreferably, cis-polybutadiene having a weight-average molecular weightof from about 100,000 to about 500,000 is employed. Along this line, ithas been found that the high cis-polybutadiene manufactured and sold byShell Chemical Co., Houston, Tex., under the tradename Cariflex BR-1220,and the polyisoprene available from Muehlstein, H & Co., Greenwich,Connecticut under the designation “SKI 35” are particularly well suited.

[0024] The unsaturated carboxlic acid component of the core composition(a co-crosslinking agent) is the reaction product of the selectedcarboxylic acid or acids and an oxide or carbonate of a metal such aszinc, magnesium, barium, calcium, lithium, sodium, potassium, cadmium,lead, tin, and the like. Preferably, the oxides of polyvalent metalssuch as zinc, magnesium and cadmium are used, and most preferably, theoxide is zinc oxide.

[0025] Exemplary of the unsaturated carboxylic acids which find utilityin the present core compositions are acrylic acid, methacrylic acid,itaconic acid, crotonic acid, sorbic acid, and the like, and mixturesthereof. Preferably, the acid component is either acrylic or methacrylicacid. Usually, from about 20 to about 50, and preferably from about 25to about 35 parts by weight of the carboxylic acid salt, such as zincdiacrylate, is included in the core composition. The unsaturatedcarboxylic acids and metal salts thereof are generally soluble in theelastomeric base, or are readily dispersible.

[0026] The free radical initiator included in the core composition isany known polymerization initiator (a co-crosslinking agent) whichdecomposes during the cure cycle. The term “free radical initiator” asused herein refers to a chemical which, when added to a mixture of theelastomeric blend and a metal salt of an unsaturated, carboxylic acid,promotes crosslinking of the elastomers by the metal salt of theunsaturated carboxylic acid. The amount of the selected initiatorpresent is dictated only by the requirements of catalytic activity as apolymerization initiator. Suitable initiators include peroxides,persulfates, azo compounds and hydrazides. Peroxides which are readilycommercially available are conveniently used in the present invention,generally in amounts of from about 0.1 to about 10.0 and preferably inamounts of from about 0.3 to about 3.0 parts by weight per each 100parts of elastomer.

[0027] Exemplary of suitable peroxides for the purposes of the presentinvention are dicumyl peroxide, n-butyl 4,4′-bis (butylperoxy) valerate,1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane, di-t-butyl peroxideand 2,5-di-(t-butylperoxy)-2,5 dimethyl hexane and the like, as well asmixtures thereof. It will be understood that the total amount ofinitiators used will vary depending on the specific end product desiredand the particular initiators employed.

[0028] Examples of such commercial availale peroxides are Luperco 230 or231 XL, a peroxyketal manufactured and sold by Atochem, LucidolDivision, Buffalo, N.Y., and Trigonox 17/40 or 29/40, al,1-di-(t-butylperoxy)-3,3,5-trimethyl cyclohexane sold by Akzo ChemieAmerica, Chicago, Ill. The one hour half life of Luperco 231 XL is about112° C., and the one hour half life of Trigonox 29/40 is about 129° C.

[0029] The core compositions of the present invention may additionallycontain any other suitable and compatible modifying ingredientsincluding, but not limited to, metal oxides, fatty acids, anddiisocyanates. For example, Papi 94, a polymeric diisocyanate, commonlyavailable from Dow Chemical Co., Midland, Mich., is an optionalcomponent in the rubber compositions. It can range from about 0 to 5parts by weight per 100 parts by weight rubber (phr) component, and actsas a moisture scavenger.

[0030] Various activators may also be included in the compositions ofthe present invention. For example, zinc oxide and/or magnesium oxideare activators for the polybutadiene. The activator can range from about2 to about 30 parts by weight per 100 parts by weight of the rubbers(phr) component.

[0031] Moreover, filler-reinforcement agents may be added to thecomposition of the present invention. Since the specific gravity ofpolypropylene powder is very low, and when compounded, the polypropylenepowder produces a lighter molded core, large amounts of higher gravityfillers may be added. Additional benefits may be obtained by theincorporation of relatively large amounts of higher specific gravity,inexpensive mineral fillers such as calcium carbonate. Such fillers asare incorporated into the core compositions should be in finely dividedform, as for example, in a size generally less than about 30 mesh andpreferably less than about 100 mesh U.S. standard size. The amount ofadditional filler included in the core composition is primarily dictatedby weight restrictions and preferably is included in amounts of fromabout 10 to about 1.00 parts by weight per 100 parts rubber.

[0032] The preferred fillers are relatively inexpensive and heavy andserve to lower the cost of the ball and to increase the weight of theball to closely approach the U.S.G.A. weight limit of 1.620 ounces.Exemplary fillers include mineral fillers such as limestone, silica,mica barytes, calcium carbonate, or clays. Limestone is groundcalcium/magnesium carbonate and is used because it is an inexpensive,heavy filler.

[0033] As indicated, ground flash filler may be incorporated and ispreferably 20 mesh ground up center stock from the excess flash fromcompression molding. It lowers the cost and may increase the hardness ofthe ball.

[0034] Fatty acids or metallic salts of fatty acids may also be includedin the compositions, functioning to improve moldability and processing.Generally, free fatty acids having from about 10 to about 40 carbonatoms, and preferably having from about 15 to about 20 carbon atoms, areused. Exemplary of suitable fatty acids are stearic acid and linoleicacids, as well as mixtures thereof. Exemplary of suitable metallic saltsof fatty acids include zinc stearate. When included in the corecompositions, the fatty acid component is present in amounts of fromabout 1 to about 25, preferably in amounts from about 2 to about 15parts by weight based on 100 parts rubber (elastomer).

[0035] It is preferred that the core compositions include stearic acidas the fatty acid adjunct in an amount of from about 2 to about 5 partsby weight per 100 parts of rubber.

[0036] Diisocyanates may also be optionally included in the corecompositions when utilized, the diioscyanates are included in amounts offrom about 0.2 to about 5.0 parts by weight based on 100 parts rubber.Exemplary of suitable diisocyanates is 4,4′-diphenylmethane diisocyanateand other polyfunctional isocyanates know to the art.

[0037] Furthermore, the dialkyl tin difatty acids set forth in U.S. Pat.No. 4,844,471, the dispersing agents disclosed in U.S. Pat. No.4,838,556, and the dithiocarbonates set forth in U.S. Pat. No. 4,852,884may also be incorporated into the polybutadiene compositions of thepresent invention. The specific types and amounts of such additives areset forth in the above identified patents, which are incorporated hereinby reference.

[0038] The golf ball core compositions of the invention are generallycomprised of the addition of about 1 to about 100 parts by weight ofparticulate polypropylene resin (preferably about 10 to about 100 partsby weight polypropylene powder resin) to core compositions comprised of100 parts by weight of a base elastomer (or rubber) selected frompolybutadiene and mixtures of polybutadiene with other elastomers, 20 to50 parts by weight of at least one metallic salt of an unsaturatedcarboxylic acid, and 1 to 10 parts by weight of a free radicalinitiator. More preferably, the particulate polypropylene resin utilizedin the present invention comprises from about 20 to about 40 parts byweight of a polypropylene powder resin such as that trademarked and soldby Amoco Chemical Co. under the designation “6400 P”, “7000 P” and “7200P”. The ratios of the ingredients may vary and are best optimizedempirically.

[0039] As indicated above, additional suitable and compatible modifyingagents such as fatty acids, and secondary additives such as Pecan shellflour, ground flash (i.e. grindings from previously manufactured coresof substantially identical construction), barium sulfate, zinc oxide,etc. may be added to the core compositions to increase the weight of theball as necessary in order to have the ball reach or closely approachthe U.S.G.A. weight limit of 1.620 ounces.

[0040] In producing golf ball cores utilizing the present compositions,the ingredients may be intimately mixed using, for example, two rollmills or a Banbury mixer until the composition is uniform, usually overa period of from about 5 to about 20 minutes. The sequence of additionof components is not critical. A preferred blending sequence is asfollows.

[0041] The elastomer, polypropylene powder resin, fillers, zinc salt,metal oxide, fatty acid, and the metallic dithiocarbamate (if desired),surfactant (if desired), and tin difatty acid (if desired), are blendedfor about 7 minutes in an internal mixer such as a Banbury mixer. As aresult of shear during mixing, the temperature rises to about 200° F.The initiator and diisocyanate are then added and the mixing continueduntil the temperature reaches about 220° F. whereupon the batch isdischarged onto a two roll mill, mixed for about one minute and sheetedout.

[0042] The sheet is then placed in a Barwell preformer and slugs areproduced. The slugs are then subjected to compression molding at about320° F. for about 14 minutes. After molding and cooling, the coolingeffected at room temperature for about 4 hours, the molded cores aresubjected to a centerless grinding operation whereby a thin layer of themolded core is removed to produce a round core having a diameter of1.545 inches.

[0043] The mixing is desirably conducted in such a manner that thecomposition does not reach incipient polymerization temperatures duringthe blending of the various components.

[0044] Usually the curable component of the composition will be cured byheating the composition at elevated temperatures on the order of fromabout 275° F. to about 350° F., preferably and usually from about 290°F. to about 325° F., with molding of the composition effectedsimultaneously with the curing thereof. The composition can be formedinto a core structure by any one of a variety of molding techniques,e.g. injection, compression, or transfer molding. When the compositionis cured by heating, the time required for heating will normally beshort, generally from about 10 to about 20 minutes, depending upon theparticular curing agent used. Those of ordinary skill in the artrelating to free radical curing agents for polymers are conversant withadjustments of cure times and temperatures required to effect optimumresults with any specific free radical agent.

[0045] After molding, the core is removed from the mold and the surfacethereof, preferably treated to facilitate adhesion thereof to thecovering materials. Surface treatment can be effected by any of theseveral techniques known in the art, such as corona discharge, ozonetreatment, sand blasting, and the like. Preferably, surface treatment iseffected by grinding with an abrasive wheel.

[0046] The core is converted into a golf ball by providing at least onelayer of covering material thereon, ranging in thickness from about0.050 to about 0.250 inch and preferably from about 0.060 to about 0.090inch. The cover composition preferably is made from ethylene-acrylicacid or ethylene-methacrylic acid copolymers neutralized with mono orpolyvalent metals such as sodium, potassium, lithium, calcium, zinc, ormagnesium.

[0047] The ionic copolymers used to produce the cover compositions maybe made according to known procedures, such as those in U.S. Pat. No.3,421,766 or British Patent No. 963,380, with neutralization effectedaccording to procedures disclosed in Canadian Patent No. 674,595 and713,631, wherein the ionomer is produced by copolymerizing the olefinand carboxylic acid to produce a copolymer having the acid unitsrandomly distributed along the polymer chain. The ionic copolymercomprises one or more α-olefins and from about 9 to about 15 weightpercent of α,β-ethylenically unsaturated mono- or dicarboxylic acid, thebasic copolymer neutralized with metal ions to the extent desired.

[0048] At least 18% of the carboxylic acid groups of the copolymer areneutralized by the metal ions, such as sodium, potassium, zinc, calcium,magnesium, and the like, and exist in the ionic state.

[0049] Suitable olefins for use in preparing the ionomeric resinsinclude,. but are not limited to, ethylene, propylene, butene-1,hexene-1, and the like. Unsaturated carboxylic acids include, but arenot limited to, acrylic, methacrylic, ethacrylic, α-chloroacrylic,crotonic, maleic, fumaric, itaconic acids, and the like. Preferably, theionomeric resin is a copolymer of ethylene with acrylic and/ormethacrylic acid, such as those disclosed in U.S. Pat. Nos. 4,884,814;4,911,451; 4,986,545 and 5,098,105, incorporated herein by reference.

[0050] In this regard, the ionomeric resins sold by E.I. DuPont deNemours Company under the trademark “Surlyn®”, and the ionomer resinssold by Exxon Corporation under either the trademark “Escor®” or thetradename “Iotek” are examples of commercially available ionomericresins which may be utilized in the present invention. The ionomericresins sold formerly under the designation “Escor®” and now under thenew name “Iotek”, are very similar to those sold under the “Surlyn®”trademark in that the “lotek” ionomeric resins are available as sodiumof zinc salts of poly(ethylene acrylic acid) and the “Surlyn” resins areavailable as zinc or sodium salts of poly(ethylene methacrylic acid). Inaddition various blends of “Iotek” and “Surlyn®” ionomeric resins, aswell as other available ionomeric resins, may be utilized in the presentinvention.

[0051] In the embodiments of the invention that are set forth below inthe Examples, the cover included acrylic acid ionomer resin having thefollowing compositions: % weight Iotek 4000 (7030)¹ 52.4 Iotek 8000(900)² 45.3 Unitane 0-110³ 2.25 Ultramarine blue⁴ 0.0133 Santonox R⁵0.0033

[0052] The covered golf ball can be formed in any one of the severalmethods known to the art. For example, the molded core may be placed inthe center of a golf ball mold and the ionomeric resin-containing covercomposition injected into and retained in the space for a period of timeat a mold temperature of from about 40° F. to about 120° F.

[0053] Alternatively, the cover composition may be injection molded atabout 300° F. to about 450° F. into smooth-surfaced hemisphericalshells, a core and two such shells placed in a dimpled golf ball moldand unified at temperatures on the order of from about 100° F. to about200° F.

[0054] The golf ball produced is then painted and marked, painting beingeffected by spraying techniques.

[0055] The present invention is further illustrated by the followingexamples in which the parts of the specific ingredients are by weight.It is to be understood that the present invention is not limited to theexamples, and various changes and modifications may be made in theinvention without departing from the spirit and scope thereof.

EXAMPLE 1

[0056] Using the ingredients tabled below, golf ball cores having afinished diameter of about 1.540 to about 1.545 inches were produced bycompression molding and subsequent removal of a surface layer bygrinding. Each core was formulated using 100 parts elastomer (rubber).In the formulations, the amounts of remaining ingredients are expressedin parts by weight, and the degrees of coefficient of restitution andcompression achieved are set forth below. The data for these examplesare the averages for twelve cores which were produced for each example.The properties of the molded cores produced from each formulation weremeasured according to the following parameters:

[0057] Riehle compression is a measurement of the deformation of a golfball in inches under a fixed static load of 200 pounds.

[0058] Coefficient of restitution (C.O.R.) was measured by firing theresulting golf ball in an air cannon at a velocity of 125 feet persecond against a steel plate which is positioned 12 feet from the muzzleof the cannon. The rebound velocity was then measured. The reboundvelocity was divided by the forward velocity to give the coefficient ofrestitution. TABLE 1 Effect of the Addition of Polypropylene PowderResin on the Properties of the Molded Core Formulations 1 2 3 4 5 6 7 8Ingredients BR-1220¹ 90 90 90 90 90 90 90 90 SKI-35² 10 10 10 0 10 10 1010 ZDA³ 31 31 31 31 27 23 23 23 ZnO 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 ZincStearate 15 15 15 15 15 15 15 15 Limestone 18 18 18 18 18 18 28 38 GrdFLash 20 20 20 20 20 20 20 20 6400 P⁴ 0 20 30 40 30 30 30 30 Trig 17/40⁵1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Papi 94⁶ .5 .5 .5 .5 .5 .5 .5 .5 Total192.0 212.0 222.0 232.0 218.0 214.0 224.0 234.0 Properties Molded CoreSize, inches 1.539 1.539 1.538 1.539 1.540 1.540 1.540 1.540 Wgt., grams36.5 35.6 35.1 34.8 35.0 34.6 35.6 36.7 Comp. (Riehle) .064 .057 .056.054 .060 .065 .065 .062 {overscore (e)} (C.O.R.) .796 .783 .773 .763.767 .760 .752 .747 Molded Ball Size, inches 1.683 1.683 1.682 1.6831.683 1.683 1.683 1.683 Wgt., grams 45.4 44.5 44.1 43.7 43.3 43.4 44.545.4 Comp. (Riehle) .050 .040 .037 .037 .045 .054 .051 .050 {overscore(e)} (C.O.R.) .811 .796 .787 .777 .785 .780 .775 .767

[0059] TABLE 2 Effect of the Addition of Polypropylene Powder Resin asthe Properties of the Molded Core Formulations Ingredients 9 10 11 12 13BR-1220 90 90 90 90 90 SKI-35 10 10 10 10 10 ZDA 31 31 29 27 25 ZnO 6.06.0 6.0 6.0 6.0 Zinc Stearate 15 15 15 15 15 Limestone 18 18 22 26 32Grd Flash 20 20 20 20 20 6400 P 0 1 5 10 20 Trig 17/40 1.5 1.5 1.5 1.51.5 Papi 94 .5 .5 .5 .5 .5 Total 192.0 193.0 199.0 206.0 220.00 Cost/lbvs. No. 9 — −$.0010 −$.0266 −$.0470 −$.0761 Properties Molded Core Size,inches 1.541 1.540 1.539 1.542 1.542 Wgt., grams 36.7 36.6 36.6 37.336.7 Comp. (Riehle) .063 .064 .065 .057 .064 {overscore (e)} (C.O.R.).796 .793 .785 .787 .759 Molded Ball Size, inches 1.683 1.683 1.6831.683 1.684 Wgt., grams 45.2 45.3 45.3 45.9 45.3 Comp. (Riehle) .053.053 .053 .048 .053 {overscore (e)} (C.O.R.) .811 .810 .802 .798 .780Ingredients 14 15 16 17 18 19 20 21 BR-1220 90 90 90 90 90 90 90 90SKI-35 10 10 10 10 10 10 10 10 ZDA 23 21 20 20 19 18 17 16 ZnO 6.0 6.06.0 6.0 6.0 6.0 6.0 6.0 Zinc 15 15 15 15 15 15 15 15 Stearate Limestone38 44 50 55 60 65 70 75 Grd Flash 20 20 20 20 20 20 20 20 6400 P. 30 4050 60 70 80 90 100 Trig 17/40 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Papi 94 .5.5 .5 .5 .5 .5 .5 .5 Total 234.0 248.0 263.0 278.0 292.0 306.0 320.0334.0 Cost/lb vs. −$.1014 −$.1238 −$.1436 −$.1497 −$.1616 −$.1725−$.1824 4.1914 No. 9 Properties Molded Core Size, 1.543 1.544 1.5441.542 1.545 1.545 1.547 1.546 Inches Wgt., grams 37.0 36.9 37.0 36.936.9 36.8 36.8 37.0 Comp. .062 .064 .063 .061 .062 .063 .061 .061(Riehle) {overscore (e)} (C.O.R.) .744 .720 .705 .695 .682 .648 .636.635 Molded Ball Size, 1.683 1.684 1.684 1.684 1.683 1.684 1.683 1.682inches Wgt., grams 45.4 45.4 45.4 45.4 45.3 45.3 45.2 45.3 Comp. .053.054 .052 .053 .052 .053 .053 .053 (Riehle) {overscore (e)} (C.O.R.).767 .750 .735 .721 .708 .695 .688 .674

[0060] As it can be seen in Formulations 1-4, the inclusion of thepolypropylene powder resin (unfluxed) to polybutadiene core compositionshas the effect of producing lighter, harder and slower molded cores. Asa result of the increase hardness, the amount of the zinc diacrylatecrosslinking agent utilized can be reduced in order to soften the moldedcores to a normal compression. See Formulations 5-8.

[0061] Moreover, because the specific gravity of polypropylene is verylow and the polypropylene powder resin produces a lighter core whenmolded, large amounts of higher specific gravity mineral fillers such aslimestone can be added. Consequently, the addition of the polypropylenepowder resin (from 20 to 40 phr in Table 1) allows for a reduction inthe amount of crosslinking agent utilized and an increase in the amountof filler while maintaining the proper weight and compression of themolded cores. In Table 1, Formulation 8 is the preferred embodiment.

[0062] Formulations 9-21 set forth in Table 2 further demonstrate theeffect produced by the addition of the polypropylene powder resin (from1 to 100 phr). As the amount of polypropylene is increased, the amountof the zinc diacrylate crosslinking agent is decreased while the amountof mineral filler (i.e. limestone) is substantially increased (i.e. forexample, in Table 2 an increase in 10 phr of polypropylene powderresulted in a reduction of about 1.5 phr ZDA and an increase of about5.7 phr mineral filler). Due to the decrease in resilience (i.e. C.O.R.)also produced by the addition of the polypropylene powder resin,Formulation 14 is the more preferred embodiment (i.e. optimal hardnessand weight as well as C.O.R.) of the invention.

[0063] Furthermore, from a product cost perspective, the addition of thepolypropylene powder (i.e. about $0.36/lb.), and the resulting reductionin the amount of the very expensive crosslinking agent utilized (such aszinc diacrylate), and in turn the increase in the amount of inexpensivemineral fillers (such as limestone at $0.04/lb.), the overall cost ofthe molded cores are substantially lowered while the proper weight andcompression is maintained. This is also exhibited in the Formulationsset forth in Table 2. TABLE 3 Comparison of the Addition of Various LowSpecific Gravity Powdered Plastics On the Properties of the Molded CoresFormulations 22 23 24 25 26 27 28 Ingredients BR-1220 100 100 100 100100 100 100 ZDA 25 25 25 25 25 25 25 Grd Flash 20 20 20 20 20 20 20 ZnO5.0 5.0 5.0 5.0 5.0 5.0 5.0 Zinc 5 15 15 15 15 15 15 Stearate Verflake25 25 25 25 25 25 25 Polyester 0 25 0 0 0 0 0 70 Mesh Nylon 0 0 25 0 0 00 70 Mesh Texture 3388 0 0 0 25 0 0 0 6800 P 0 0 0 0 25 0 0 7200 P 0 0 00 0 25 0 Huntsman 0 0 0 0 0 0 25 P.P. 170 231 XL 0.90 0.90 0.90 0.900.90 0.90 0.90 Papi 0.50 0.50 0.50 0.50 0.50 0.50 0.50 Progerties MoldedCore Wgt., grams 37.0 37.2 36.7 36.0 35.7 35.7 35.8 Comp. 74 58 64 78 5554 55 (Riehle) {overscore (e)} (C.O.R.) .786 .773 .753 .732 .771 .770.767

[0064] The data demonstrates that the addition of the polypropylenepowder resin produces enhanced effects (i.e. produces a lighter andharder molded core) than the remaining powdered thermoplastics tested.While a number of the powdered plastics did show some enhancement inhardness, the increased hardness was not as significant as thatdemonstrated by present invention and/or the addition of the powderedplastics lead to an increase in weight upon molding and/or a substantialreduction in resiliency was noted. Similar results were also observedthrough the addition of powdered polymethyl methacrylate, powderedpolyethylene, powdered polystyrene etc. to conventional corecompositions. Consequently, the additional powdered plastics failed toexhibit the enhanced effects (i.e. the production of a lighter andharder molded core) exhibited by the present invention.

[0065] The invention has been described with reference to the preferredembodiments. Obviously, modifications and alterations will occur toothers upon reading and understanding the preceding detaileddescription. It is intended that the invention be construed as includingall such alterations and modifications insofar as they come within thescope of the claims and the equivalents thereof.

Having thus described the preferred embodiment, the invention is nowclaimed to be:
 1. An improved core composition for a golf ball, saidcomposition comprising a base elastomer selected from polybutadiene andmixtures of polybutadiene with other elastomers, said polybutadienehaving a molecular weight of from about 50,000 to about 500,000, atleast one metallic salt of an α,β-ethylenically unsaturatedmonocarboxylic acid, a free radical initiator, and a polypropylenepowder resin.
 2. The composition as defined in claim 1 , wherein saidpolypropylene powder resin has a specific gravity of about 0.90 g/cm³and a melt flow rate of about 4 to about
 12. 3. The composition asdefined in claim 1 , wherein said polypropylene powder resin enhancesthe hardness of the core composition thereby reducing the amount ofmetallic salt of an α,β-ethylenically unsaturated monocarboxylic acidincorporated into the core composition.
 4. The composition as defined byclaim 1 , further comprising a modifying ingredient selected fromfillers, fatty acids, metal oxides, and mixtures thereof.
 5. Thecomposition as defined in claim 4 , wherein said polypropylene powderresin enhances the hardness of the core composition without an increasein weight thereby reducing the amount of metallic salt of anα,β-ethylenically unsaturated monocarboxylic acid and increasing theamount of a mineral filler incorporated into the core compositions. 6.The composition as defined in claim 1 , wherein said core compositioncomprises from about 10 to about 100 parts by weight of thepolypropylene powder resin based on 100 parts by weight elastomer. 7.The composition as defined in claim 1 , wherein said core compositioncomprises from about 20 to about 40 parts by weight of the polypropylenepowder resin based on 100 parts by weight elastomer.
 8. In a corecomposition for a golf ball comprising a base elastomer selected frompolybutadiene and mixtures of polybutadiene with other elastomers, atleast one metallic salt of an α,β-ethylenically unsaturatedmonocarboxylic acid, a free radical initiator, and a filler, theimprovement comprises adding a low specific weight polypropylene powderresin to increase the hardness without increasing the weight of the corecomposition thereby reducing the amount of metallic salt of anα,β-ethylenically unsaturated monocarboxylic acid and increasing theamount of filler included in the core composition.
 9. The improvedcomposition of claim 8 , wherein said polypropylene powder resin has aspecific gravity of about 0.90 g/cm³, a melt flow rate of about 4 toabout 12 and a particle size distribution at 20 mesh of about 99percent.
 10. The improved composition of claim 8 , wherein said corecomposition comprises from about 10 to about 100 parts by weight of thepolypropylene powder resin based as 100 parts by weight elastomer. 11.The improved composition of claim 8 , wherein said core compositioncomprises from about 20 to about 40 parts by weight of the polypropylenepowder resin based as 100 parts by weight elastomer.
 12. In a corecomposition for a golf ball comprising a base elastomer selected frompolybutadiene and mixtures of polybutadiene with other elastomers, fromabout 20 to about 50 parts per weight elastomer of at least one metallicsalt of an unsaturated carboxylic acid, from about 1 to about 10 partsper weight elastomer of a free radical initiator, and from about 0 toabout 50 parts per weight elastomer of a filler additive, theimprovement comprises adding from about 10 to about 100 parts per weightelastomer of a low specific weight polypropylene powder resin toincrease the hardness of the core composition thereby decreasing theamount of metallic salt of an unsaturated carboxylic acid included inthe core composition.
 13. The improved composition of claim 12 , whereinsaid polypropylene powder has a specific gravity of about 0.90 g/cm³, amelt flow rate of about 4 to about 12 and is in a particle form lessthan 20 mesh.
 14. A method of decreasing the amount of a metallic saltof an unsaturated carboxylic acid present in the core composition havinga base elastomer selected from polybutadiene and mixtures ofpolybutadiene with other elastomers, at least one metallic salt of anα,β-ethylenically unsaturate monocarboxylic acid and a free radicalinitiator, said method comprising the step of adding to the corecomposition a polypropylene powder resin.
 15. The method of claim 14 ,wherein said polypropylene powder has a specific gravity of about 0.90g/cm³ and a melt flow rate of about 4 to about
 12. 16. A method fordecreasing the amount of a metallic salt of an unsaturated carboxylicacid and increasing the amount of a mineral filler in a core compositionhaving a base elastomer selected from polybutadiene and mixtures ofpolybutadiene with other elastomers, at least one metallic salt of anunsaturated carboxylic acid, a free radical initiator and a mineralfiller, said method comprising the step of adding to the corecomposition a polypropylene powder resin.
 17. A method of claim 16 ,wherein said polypropylene powder has a specific gravity of about 0.90and a melt flow rate of about 4 to about 12.